As for a general electrographic method, a method for obtaining a copied material by forming a latent image on an image bearing member (photosensitive drum), visualizing the latent image by supplying a toner to the latent image, transferring the resulting toner image to a transfer material, e.g., paper, and thereafter, fixing the toner image on the transfer material by heat/pressure is known.
For example, in the electrophotography, a photo conductor-shaped drum, which serves as a photosensitive drum, through the use of a photoconductive substance is subjected to a charging treatment uniformly to have predetermined polarity and potential and is subjected to image pattern exposure, so that an electrostatic latent image is formed. Thereafter, development is performed with a toner and the resulting image is transferred and fixed to a transfer medium, e.g., paper, in general. After the transfer step, the toner remaining on the photosensitive drum is removed by some method. Blade cleaning is mentioned as a removal method employed most frequently. This is a method to scrape the toner by pressing a blade-shaped member, e.g., rubber, having elasticity against a photosensitive drum surface.
A spherical toner having a sharp particle size distribution and serving as the toner used for such an electrophotograph has characteristics, e.g., excellent transferability and thin line reproducibility. On the other hand, in a system to clear the toner from the photosensitive drum, cleaning becomes difficult as the circularity increases. One of the reasons is considered to be that rolling of the toner occurs because of high circularity and the toner slips through a contact nip between the cleaning blade and the photo conductor easily.
As for a measure to prevent poor cleaning with respect to the spherical toner, for example, in a cleaning apparatus of a blade system, it has been attempted to prevent slipping through of the spherical toner by increasing the linear pressure applied to an edge portion of a blade. However, this measure on the basis of merely an increase in linear pressure has problems that, for example, chipping of a blade edge portion is facilitated, an unusual sound occurs because of chatter vibrations, or abrasion of the photo conductor due to contact of a blade is facilitated.
PTL 1 proposes a method in which an external additive is retained on an blade edge portion to form an inhibition layer and, thereby, toner particles are blocked to stabilize cleaning. According to this method, the external additive to form the inhibition layer slip through the blade, so that a charge member is contaminated. Consequently, it is necessary that a mechanism to clean the charge member be disposed, the mechanism becomes complicated, and an increase in the cost is caused.
PTL 2 proposes a measure to reduce a toner remaining after transfer and improve cleanability through reduction in the adhesion by embedding an external additive into a spherical toner. However, it is difficult to obtain sufficient cleanability of the toner with high circularity.